Dosing Begins in Trial of Efanesoctocog Alfa in Boys With Severe Hemophilia A

A first patient has been dosed in XTEND-Kids, a Phase 3 clinical trial evaluating the safety and efficacy of the investigational replacement therapy efanesoctocog alfa in boys with severe hemophilia A.

Hemophilia A is caused by the lack of a functional blood clotting protein called factor VIII (FVIII). Replacement therapies for hemophilia A work by providing patients with the missing FVIII protein.

Efanesoctocog alfa, formerly BIVV001, is a potentially longer-lasting replacement therapy for hemophilia A being jointly developed by Sanofi and Sobi.

It contains a version of FVIII that has been fused to parts of other proteins (namely von Willebrand factor and XTEN), in order to allow the therapy to work longer in the body, requiring less frequent dosing. Efanesoctocog alfa is designed to be administered once weekly, when given as a prophylactic, or preventive, treatment to prevent spontaneous bleeds.

“Efanesoctocog alfa has the potential to advance the treatment of people with haemophilia A,” Ravi Rao, head of research and development and chief medical officer at Sobi, said in a press release.

Data from a previous Phase 1/2 trial, called EXTEN-A (NCT03205163), showed that a single dose of efanesoctocog alfa was able to safely and effectively increase FVIII activity levels in men with severe hemophilia A.

The open-label XTEND-Kids trial (NCT04759131), sponsored by Sanofi, aims to enroll about 65 boys, ages 12 and younger, with severe hemophilia A who have used other FVIII treatments.

All will be given the investigational therapy, which will be administered intravenously (directly into the bloodstream), once weekly for 52 weeks (about a year). Those who complete the trial may choose to continue treatment in a planned extension phase.

The trial’s primary goal is to assess the development of inhibitors — neutralizing antibodies targeting FVIII, which are produced when the body’s immune system mistakenly sees the replacement therapy as a threat. Inhibitors can reduce the effectiveness of these treatments.

It will also assess the therapy’s safety and efficacy at lowering the number of spontaneous and traumatic bleeds, and its pharmacokinetic profile, meaning how the medication moves through the body.

XTEND-Kids is currently enrolling eligible patients at centers in Pittsburgh, Pennsylvania; Le Kremlin-Bicêtre, in France; and Madrid. Additional information is available here.

“The initiation of the phase 3 development in the paediatric population is a demonstration of Sobi’s continued commitment to enable higher standards for people living with haemophilia A,” Rao said.

Sanofi is also sponsoring another open-label Phase 3 trial, called XTEND-1 (NCT04161495), that aims to assess the safety and efficacy of the therapy in this patient group ages 12 and older. XTEND-1 is recruiting at three locations in the U.S.; more information is available here.

Efanesoctocog alfa was recently granted fast track designation by the U.S. Food and Drug Administration (FDA) to speed its development and review. The therapy has also been designated an orphan drug by the FDA and the European Commission.